Gene therapy involves the transfer of genetic material encoding one or more therapeutic genes and the sequences necessary for their expression to target cells to alter their genetic makeup for some desired therapeutic effect. Gene therapy is being tested in a wide variety of applications, including the treatment of complex genetic disorders such as cancer and infectious diseases such as AIDS, and in tissue engineering. Often, the genetic material is transferred ex vivo to tissue that has been removed from a patient. After gene transfer, the tissue is cultured and expanded in vitro, and then re-implanted into the patient. If the target tissue cannot be removed or cultured in vitro (e.g., brain, heart, lungs), the genetic material is instead injected directly into the patient.
Recombinant retroviruses are the most common gene transfer vector used in human gene therapy clinical trials. However, transduction efficiency is often too low to achieve the desired biological effect in many potential human gene therapy situations. Attempts to improve transduction efficiency by concentrating the retroviruses (e.g., by centrifugation, ultrafiltration, tangential flow, or hollow fiber filtration) have not been very successful. Although retrovirus preparations concentrated by these methods contain higher concentrations of infectious virus, they nonetheless do not transduce significantly more target cells than the unconcentrated stocks. The development of methods that improve transduction efficiency is therefore necessary.
Methods for increasing the sensitivity of assays used to detect disease-causing viruses are also needed. The number of viral particles in a patient's tissue (i.e., viral load) generally correlates well with the rate of progression of associated diseases. To obtain earlier and more accurate diagnoses, and thereby improve patient prognosis, medical personnel need to be able to detect lower viral loads than can be detected with the analytical methods that are currently in widespread use.